A typical mass flow controller (MFC) is a closed-loop device that sets, measures, and controls the flow of a gas in industrial processes such as thermal and dry etching among other processes. An important part of a MFC is a sensor that measures the mass flow rate of the gas flowing through the device. Typically, a closed-loop control system of the MFC compares an output signal from the sensor with a predetermined set point and adjusts a control valve to maintain the mass flow rate of the gas at the predetermined set point.
The closed-loop system performs well when valve is relatively close to required position and its movement changes the flow, so that the algorithm immediately sees flow response and adjusts valve position accordingly. When a MFC is at zero set point (zero valve position), and then is given non-zero set point, it takes a long time for valve to move from zero position to a position where noticeable flow appears and closed-loop algorithm starts working properly. This results in long response delay and poor performance of the MFC. And to date, attempts to improve a response time of the MFC have been unsuccessful or are otherwise unsatisfactory.